(a) Field of the Invention
The present invention relates to silver halide photographic materials, and more particularly to silver halide photographic materials excellent in rapid processability, low in fogging, and high in sensitivity and contrast.
(b) Description of the Prior Art
Currently commercially-available silver halide photographic materials (hereinafter referred to as photographic materials), and methods of forming images using them are various, and examples of their use can be found in a variety of fields. In many cases the composition of the silver halide emulsions used in these photographic materials consists of silver bromoiodide, silver bromochloride, or silver chlorobromide, these being mainly composed of silver bromide to provide high contrast.
Of the color photographic materials, especially regarding such products as photographic papers, used in a market where there is great demand for prints to be processed and delivered in a short time, to meet the requirement of increased developing speed, silver bromide or silver chlorobromide substantially free from iodide has been used. However, even in this case, many times silver bromide was used as a main component to obtain the required sensitivity.
In recent years the demand for rapid processability of color photographic paper has increased more and more, and many studies have therefore been made and some techniques to attain this rapid processability have been reported. In particular, it is well known that when the silver chloride content in a silver halide emulsion is increased, the developing speed can be remarkably improved. However, when an emulsion with a high silver content, that is, a so-called high-silver-chloride emulsion, is used, there is a tendency toward fogging, and it is difficult to obtain high sensitivity. Therefore, although the above technique is excellent in developing speed, there is a requirement to overcome these defects to make high-silver-chloride emulsions practical.
As mentioned above, the development of silver halide emulsions high in developing speed is one of the most important techniques for providing photographic materials that are adaptable to rapid processing, and to attain this it is necessary to provide high-silver-chloride emulsions with high sensitivity without causing fogging.
As techniques for increasing the sensitivity of silver chlorobromide emulsions high in silver chloride content, some reports can be found.
For example, Japanese Patent Application (OPI) Nos. 95736/1983 and 108533/1983 disclose techniques directed to high-silver-chloride emulsions that have a layered-type structure. According to Japanese Patent Application (OPI) No. 95736/1983, although an emulsion that can be subjected to rapid processing and is high in sensitivity can be obtained by allowing a layer mainly composed of silver bromide to be present inside the grains, it was found that in actual practice when pressure is applied to the emulsion grains, the desensitization becomes too great for the emulsion to be of practical use. Further, according to Japanese Patent Application (OPI) No. 108533/1983, although it is suggested that by locally-placing a layer composed mainly of silver bromide on the grain surface, an emulsion can be made that can be subjected to rapid processing, is high in sensitivity and wide in latitude of the chemical ripening, such disadvantages were found that in practice the toe of the characteristic curve is apt to become soft (in an extreme case, two-step gradation is observed), and further, that desensitization due to pressure is liable to occur. Further, Japanese Patent Application (OPI) Nos. 222844/1985 and 222845/1985 disclose techniques directed to high-silver-chloride emulsions provided with a layered-type structure. Even these techniques could not solve the above disadvantages.
Therefore, the problem that the sensitivity of silver chlorobromide emulsions having a high silver chloride content should be enhanced still remains an important theme.
Further, the performance required for these numerous photographic materials varies according to the particular application. It is necessary still to fully exhibit "high density recording", which is the most excellent characteristic of the advantages of photographic materials using silver halides, that is, the so-called silver salt photographic materials. Therefore, it goes without saying that the particular photographic material must be high in sharpness. Therefore, various techniques for enhancing sharpness have been developed in accordance with the level of sharpness required for the respective photographic material and the applied form of the photographic material, and these are applied in actual practice.
As factors in lowering the sharpness of photographic materials, two main points can be mentioned: halation due to the reflection of incident light at the emulsion layer/base interface or at the base/atmosphere interface; and irradiation due to the scattering of light by silver halide grains themselves.
To obviate lowering of the sharpness, for the former case, it is effective to provide an antihalation layer at the interface between the base and the emulsion layer or to the undersurface of the base, and for the latter case, it is effective to color the emulsion layer on the base with a dye or the like.
For the properties required for dyes for antihalation or anti-irradiation, the following must be satisfied:
(1) the dye has a spectral absorption suitable for the application; PA1 (2) the dye can be eliminated quickly in photographic processing; PA1 (3) the dye should not desensitize or fog the silver halide emulsion; and PA1 (4) the dye is stable during the production of the photographic material and during the storage of the produced photographic material. From these points of view, for example, oxonol-type dyes, and azo-type dyes are useful, and they are used in actual practice.
Generally most photographs used in the final form are images printed on photographic paper, and recently in particular the use of color photographic paper has become dominant. Although the sharpness of color images obtained as final items is, of course, largely dependent on the performance of the color negative film used, the sharpness of the color photographic paper on which the printing will be done also has a similarly large influence. That is, it can be said that, among performances required for color photographic paper, high sharpness is a very important item. For color photographic paper, since the reflective base has photographic emulsion layers thereon, it is possible to greatly enhance sharpness by preventing the irradiation mentioned above.
As can be understood from the above description, the market demand for photographic materials that can be processed rapidly and are high in sharpness is very strong. To meet this demand, one of the most important themes is that enhancement of the performance of silver halide photographic materials that have a photographic emulsion layer containing a silver chlorobromide emulsion or a silver chloride emulsion and a dye.
However, photographic materials having such a photographic emulsion layer highly change in sensitivity due to a change in humidity when exposed, and in many cases the color reproduction of a color image is remarkably deteriorated.